The thermal oxidation of a silicon nitride film was evaluated at temperatures ranging from 900°C to 1100°C and under water vapor partial pressures ranging from 0.25 atm to 0.95 atm. The oxidation rate was measured by ellipsometry and the results were compared with those of simultaneously oxidized silicon substrates. The conversion ratio, which is the thickness ratio of a grown oxide film to a consumed nitride film, of 1.64 was obtained with small fluctuation. The oxidized nitride thickness xn was found to be proportional to t2/3, where t is the oxidation time. This relationship is consistent with a proposed oxidation model. The figure of merit m was defined as the masking effect of a nitride film. It was found that a large m value was obtained when the film was oxidized at low temperature and under high water vapor partial pressure.

Abslraact. The calculauon of the torque T an a permanent ellipsoidal magnet immersed in a magnetic liquid is more delicate than one might be inclined to expect. This problem, for instance, has a bearing on fundamental discussions carried out in the past about the choice between different formulotioor of electromagnetic theory. The present paper analyses the calculation of T anew. emphasizing the relation to, and the explanation of. the imponmt experiment carded out by Whitwonh and Stopes-Roe in 1971. The outcome of the experiment is explained in r e m of stmdxd magnetastatics. based upon use of the scalar potential ). The relation to the sa-dled KennellySommerfeld eontmveny is commented upon. The physical interpretation of the situation is elucidated by -ing out in deml sn examination of the total energy balance in the special case of spherical mgnet geometry.

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